Pmasonic Dosimetry System Peformance Testing and Results at Nuclear Accident Dose Levels

Transcription

1 Pmasonic Dosimetry System Peformance Testing and Results at Nuclear Accident Dose Levels 5 RAD to 1, RAD Prepared by: Michael R. Klueber Date: April 6, 1998 COPY

2 DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employm, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, proms, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recornmendktion, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

3 Overview: Title 1 Code of Federal Regulations Part , Nuclear Accident Dosimetry, states a) Installations possessing sufficient quantities of fissile material to potentially constitute a critical mass, such that the excessive exposure of personnel to radiation from a nuclear accident is possible, shall provide nuclear accident dosimetry for those personnel. b) (1) Nuclear accident dosimetry shall include the following: A method to conduct initial screening of personnel involved in a nuclear accident to determine whether significant exposures to radiation occurred; (2) Methods and equipment for analysis of biological materials; (3) A system of fixed nuclear accident dosimeter units; and (4) Personal nuclear accident dosimeters worn by all personnel who enter locations in which criticality alarm systems are required. Panasonic thermoluminescent dosimeters (TLDs) are used as the photon dose assessment part of the personal nuclear accident dosimeter (PNAD) and may be used for the same purpose with the fixed nuclear accident dosimeter (FNAD). To demonstrate compliance with 1CFR (and, its predecessor, DOE Order l), several sets of dosimeters were irradiated to photon doses above the upper limit of the DOELAP testing standard, DOE/EH-26 and DOE/EH-27. The upper range of the test was 1, rads, using both low energy (7 kev) and high energy (662 kev and 1332 kev) sources. The testing indicated that the Panasonic TLD system is capable of meeting the requirements of 1CFR and DOE Order Procedure: Initially five standard Rocky Flats personal dosimeters were prepared for each dose level / photon energy with ten transit dosimeters. The photon energies chosen were the two energies specified in DOE/EH-26, Department of Energy Standard for the Performance Testing of Personnel Dosimetry Systems: low energy: NIST technique M15 (7 kev) and high energy: 37Cs(662 kev). The TLDs used in the dosimeters were Panasonic UD-X2AS and UD-89AS TLDs. The test dose levels for the PNAD dosimeters were 5 rads, the upper limit of the DOELAP testing, 75 rads, and 1 rads, the upper limit formerly specified for PNAD dosimeters in DOE Order The PNAD testing was performed January The test dose levels for the FNAD dosimeters were 3, rads, 6, rads, and 1, rads, the upper limit formerly specified for FNAD dosimeters in DOE Order The FNAD testing was performed in March The dosimeters were sent to Battelle Pacific Northwest National Laboratories (PNNL) for irradiation. The irradiation protocol used by PNNL followed the DOELAP requirements, with the exception of using a 6oCo source for the irradiations for the high energy photons to dose levels greater than 1, rads. The dosimeters were irradiated on PMMA phantoms, however, no testing was performed at this time to quantify the difference between free-inair and phantom response. 98pansym.doc 2

4 The PNAD test dosimeters were irradiated to the photon energies originally specified. However, after the FNAD test dosimeters were received by the PNNL staff, it was determined that dose rate of the 137Cs (662 kev) source was too low to permit timely irradiation of the dosimeters to doses above 1, rads.. We decided to use the 6oCo (1173 and 1332 kev) source since this source has a much higher dose rate. The number of dosimeters irradiated using the 6oCo source in each of the dose categories stated above was reduced from five dosimeters per category to four dosimeters per category. The number of transit dosimeters was reduced from ten to eight dosimeters. The extra five dosimeters were irradiated to 5 rem using the 6oCo source. (The average response of element 3 of the UD-82 (E3) of these five dosimeters was compared to the 5 rem calibration dosimeters' average response irradiated using the 137Csource. The average response was 2% below the delivered dose, compared with the 1% low response of the '37Cs source.) The test TLD readings were processed through the ELEM module of the ISA dose processing software to correct the element readings with Element Correction Factors (ECFs) and to subtract the transit dosimeter readings. The net element readings were processed through the standard site dose equivalent algorithm to calculate a dose for each UD-82/UD-89 TLD pair. (The standard site dose equivalent algorithm contains an Accident Category branch.) A performance quotient, Pi, was calculated for each dosimeter, using the following equation: I (Reprted)i-(De1ivered)i Pi = (De1ivered)i I The bias, B, defined as the average of the performance quotients, Pi, for n dosimeters, for a specific group of dosimeters, was computed using the following equation: The standard deviation, s, of the performance quotients, Pi, was computed for each specific group bias, B, using the following equation: Each of the equations above may be found in DOEEH-26, section 4.2. A bias, B, and standard deviation, s, were computed for each group of dosimeters, and for all dosimeters per photon energy, and for all dosimeters. The tabular results and graphs for the bias of each group by photon energy are contained in Appendix 1. Quality Assurance: Prior to reading the PNAD test TLDs in Reader 1, calibration dosimeters, irradiated at Battelle on Dec , 1997, were read to determine the condition of Reader 1. The results of the calibration dosimeters were: 98pansym.doc 3

5 , Battelle Calibration TLDs Battelle Irradiation Date: Dec , 1997 Photon Counter Ratios E2 I E3 I E5 I E7.998 I 1.6 I.956 I 1.25 Freq. Counter Ratios E I Photon Counter Ratios E2 E3 E5 E7 Before After Freq. Counter Ratios E The before calibration TLD ratios indicated that the TLD reader was working properly, however, the after calibration TLD ratios indicated that the TLD reader s response had shifted during the processing of the test TLDs The 5 rem 6oCo group TLDs had a response on element 3 (E3) that was 2% below the delivered dose, indicating that the shift was in the frequency counter. Since all the test TLD readings were from the frequency counter, the TLD responses were adjusted using the after Frequency Counter ratio. The adjusted TLD responses were processed through the algorithm to obtain the final doses that are contained in Appendix 1. Conclusion: PNAD Test TLDs: Each dosimeter was within +2% of the delivered dose, and the bias, B, for all dosimeters was.71, with a standard deviation, s, of.39. The Panasonic dosimetry system meets the requirements of 1CFR and DOE Order for use in a PNAD in determining the Gamma dose portion of the dose from a Nuclear Accident. FNAD Test TLDs: Two dosimeters were not within,2% of the delivered dose, however, the bias, B, for all dosimeters was.17, with a standard deviation, s, of.13. The Panasonic dosimetry system meets the requirements of 1CFR and DOE Order for use in a FNAD in determining the Gamma dose portion of the dose from a Nuclear Accident. 98pansym.doc 4.-

6 Appendix 1 Panasonic Dosimetry System Nuclear Accident Level Performance Results Low Energy Photon Testing Bias.67 MI5 1 rem Mi5 3rem M15 6 rem I I 1.56 I.116 I Bias I.122 I I I 1.56 I.16 I St.Dev. I.33 I Bias St. Dev , Bias pansym.doc 5

7 High Energy Photon Testing 98pansym.doc 6

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9 c Accident Dose Level Performance High Energy Photon Combined Testing (CS-137 & CO-6) Acc-1998.dOC 8

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